The energy drink business is booming. Sales in the U.S. have hit more than $10 billion, eclipsing categories such as iced tea or sports drinks. About 6 billion energy drinks were consumed nationwide in 2010, and it's estimated that 31% of teenagers drink them regularly.

It's no secret how energy drinks work: caffeine. Consider that just 2 ounces of a popular brand contains 207 mg of caffeine, which is almost as much as six cans of Coca-Cola. It is more than double the recommended amount of daily caffeine intake for teenagers, who are often targeted in advertising campaigns. Roland Griffiths, a researcher at Johns Hopkins University, rightly calls them "caffeine delivery systems."

Dietary supplements?

Most energy drinks also contain herbal ingredients such as ginkgo, taurine or milk thistle. Although scientific studies show that these additives have little value, their presence allows energy drinks to be sold as dietary supplements rather than drugs.

It's an important distinction. Supplements don't have to disclose the amounts of caffeine they contain, while over-the-counter drugs that contain similar doses of caffeine do. So in the majority of cases, those who consume energy drinks don't know how much caffeine they're ingesting.

Energy drinks can lead to serious health problems, including palpitations, rapid heart rates, dehydration, elevated blood pressures, or even heart attacks. Their high caffeine content, along with "natural" additives, can interact with prescription drugs. Worse, 56% of college students report mixing energy drinks with alcohol, which studies show increase the risk of committing or experiencing a sexual assault, riding with a drunk driver, or becoming involved in an alcohol-related car accident.

Deaths also reported

According to the recent survey by the Substance Abuse and Mental Health Services Administration, there were more than 20,000 emergency room visits involving energy drinks in 2011, double the number from 2007. Last year, the Food and Drug Administration received reports of 18 deaths and over 150 injuries that might have been associated with the drinks.

These safety concerns require energy drinks to be more closely scrutinized. Beverage manufacturers should clearly label the caffeine content. Adults should limit their caffeine intake to about 500 mg per day (or about two tall cups of Starbucks brewed coffee), less for teens and older patients and those with heart or liver problems. Doctors need to do a better job screening for and counseling those who consume high amounts of energy drinks. Finally, we should consider the approach taken by our neighboring countries.

Canada will soon cap energy drink caffeine content to 180 mg per can or bottle, which, if instituted in the U.S., would require reformulation of a substantial number of drinks. Mexico is seeking to ban the sales of energy drinks to those younger than 18.

Perhaps most effective would be to stop seeing energy drinks as beverages, and instead view them as liquid stimulant drugs. Because that's what they really are.

Kevin Pho, a primary care physician in Nashua, N.H., blogs at MedPage Today's KevinMD.com and is a member of USA TODAY's Board of Contributors.

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